A postprandial excessive blood glucose symptom is defined as the condition where the postprandial glucose level in blood increases beyond the normal range of glucose (for example, 140 mg or higher as the blood glucose level of two hours after eating), and means that the blood glucose level after ingestion of carbohydrates becomes high even for healthy people who are not diabetes patients and borderline diabetes patients. Thus, the postprandial excessive blood glucose symptom is conceptually different from an excessive casual blood glucose symptom in which the fasting blood glucose level is constantly higher than the normal level range due to diabetes.
After eating, in particular, after the ingestion of a diet containing carbohydrates, the increase of the blood glucose level generally induces the promotion of insulin secretion. Insulin mediates its action in the muscle, the liver, the fat tissue or the like, and inhibits the rapid postprandial increase of a blood glucose level. However, prolonged insulin secretion due to a continuous hyperglycemia condition leads to reduction of insulin sensitivity (insulin resistance) in target organs for insulin such as the muscle, and further, a larger amount of insulin is secreted from pancreas. Then, exhaustion of the pancreas finally occurs, and secretion of insulin from pancreatic β-cells lowers. However, each target organ for insulin remains in a state of increased insulin resistance. Thus, as is known, malfunction of the insulin action mechanism results in obesity or type II diabetes (hyperglycemia).
Further, in recent years, it has been reported that postprandial excessive blood glucose is an independent risk factor of a cardiovascular event (Non-Patent Documents 1 and 2), and it has been reported that although there is weak correlation between fasting hyperglycemia and a probability of death from a cardiovascular disease, however there is strong correlation between hyperglycemia of patients who show 200 mg/dL or higher in the level of two hours after eating in the oral glucose tolerance test (OGTT) and a probability of death from a cardiovascular disease (Non-Patent Document 2). Further, it has also been reported that when vascular endothelial cells are cultured in a hyperglycemia condition, apoptosis of the cells occurs more frequently in an intermittent hyperglycemia condition than in a continuous hyperglycemia condition (Non-Patent Document 3).
Accordingly, the postprandial excessive blood glucose symptom is not only an inducement of type II diabetes and obesity, but also a cause or a precipitating factor of various diseases such as arteriosclerosis and further hyperlipidemia, hence, prevention of the postprandial excessive blood glucose symptom is useful for prophylaxis and treatment of those diseases.
An α-glycosidase inhibitor, a rapid-acting insulin secretion accelerator, and the like are known as therapeutic agents for postprandial excessive blood glucose, and they are mainly used for severe patients in medical institutions. In contrast, a nonpharmacological therapy, which is a collective name for improvement in lifestyle habit, such as a diet therapy, an exercise therapy, and limitation of alcohol drinking and smoking, is widely applicable to subjects, from prophylaxis for normal subject to treatment of severe patients exhibiting an excessive blood glucose symptom.
Although, many of the drugs used for improving postprandial excessive blood glucose are satisfactory in their effectiveness at present, however on the other hand, concerns about prolonged use of those drugs are pointed out, because, for example, the drugs have caused adverse effects such as abdominal bloating, flatulence, flatus increase, loose stool, diarrhea, abdominal pain, and hepatic dysfunction. In addition, long-term implementation of a general therapy such as a diet therapy and an exercise therapy involves extreme difficulties. Therefore, there has been demanded a material for inhibiting the postprandial increase of blood glucose, the material having little adverse effects, being ingestible on a daily basis, and being derived from naturally occurring substances.
From the foregoing, materials derived from food have been actively searched for the purpose of inhibiting the rapid postprandial increase of blood glucose, and as a result, many active ingredients exhibiting an action of inhibiting the increase of blood glucose have been isolated and identified. Although there have been discovered foods or active ingredients thereof which seem to exhibit an action of inhibiting the increase of blood glucose, these effectiveness has not always been satisfactory.
Meanwhile, cycloartenol is biosynthetic precursor of plant sterols, and are triterpene alcohols which are distributed in latex of plants belonging to the family Euphorbiaceae, rice bran, rapeseeds, and the like.
It has been reported that cycloartenol mediates actions such as inhibition of oncogenesis promotion, an anti-inflammatory action, a cholesterol lowering action, and an action of promoting adiponectin secretion (Patent Document 1 and Non-Patent Documents 4 to 6). In addition, it has been reported that ferulic acid esters of cycloartenol exhibit an action of improving a brain function, an action of controlling an autonomic nerve function, and the like (Patent Documents 2 and 3).
However, there has been no report on the relationship between cycloartenol and postprandial excessive blood glucose.